Effects of L-glutamate and L-aspartate supplementation on systemic and intestinal immune responses of weaned piglets challenged with F18 enterotoxigenic Escherichia coli challenge

Abstract L-glutamate (Glu) and L-aspartate (Asp) are pivotal components in the cellular metabolic pathways and immune regulation of pigs. This study aimed to investigate the effects of Glu and Asp on systemic and intestinal immune responses of weaned piglets challenged with an enterotoxigenic Escherichia coli (ETEC) F18. A total of 49 weaned pigs [initial body weight (BW) = 8.18 ± 1.54 kg] were randomly assigned to one of seven treatments, with seven piglets per treatment. The treatments included negative control (NC) and positive control (PC) that were fed with control diet without or with F18 enterotoxigenic Escherichia coli (ETEC) challenge, respectively. The other five dietary treatments were supplemented with either 1% or 2% Glu or Asp, or 50 mg/kg of Carbadox, and were challenged with ETEC. All pigs except for NC were challenged with F18 ETEC orally for three consecutive days at the dose of 1010 CFU•dose-1•d-1. The study period lasted for 3 wk, with a 7-d adaptation period and 14 d post-inoculation (PI). Blood samples were collected on d 0 before ETEC inoculation, and on d 2, 5, and 14 PI to analyze systemic inflammatory markers by the enzyme-linked immunosorbent assays. On d 14 PI, intestinal mucosa from jejunum and ileum were collected to analyze the mRNA expression of inflammatory cytokines by quantitative polymerase chain reaction. All data were analyzed with ANOVA using the PROC MIXED of SAS with pig as the experimental unit. Among all treatments, pigs fed with carbadox had the least (P < 0.05) serum TNF-α, haptoglobin, and C-reactive protein throughout the experiment. Pigs supplemented with 1% Glu had similar concentrations of TNF-α, haptoglobin, and C-reactive protein, while pigs fed with 2% Asp had similar serum haptoglobin compared with pigs fed with carbadox. Compared with PC, supplementing Glu and Asp reduced (P < 0.05) the mRNA expression of IL12 in jejunal mucosa. Pigs fed with carbadox tended to have greater (P < 0.10) expression of IFNG in ileal mucosa than pigs in PC, while no difference was observed in IFNG expression among 1% Glu, 1% or 2% Asp, and carbadox groups. In addition, pigs fed with 1% Glu or 2% Asp had greater (P < 0.05) expression of IL12 in ileal mucosa than pigs in PC. However, dietary treatments did not affect the gene expression of TNFA, IL1B and TGFB in jejunal and ileal mucosa of pigs. In conclusion, results of the present study indicate that dietary supplementation of 1% Glu or 2% Asp affected both systemic and intestinal immune responses of ETEC challenged weaned pigs with similar trend as the supplementation of carbadox.